1. Field of the Invention
This invention relates generally to the art of transmitting information along a well bore drill string or other pipe. More particularly, the invention relates to a means for isolating the section of the drill string, employed for information transmission, from acoustic noise generated by the drilling process.
2. Description of the Prior Art
Many systems have been developed for acoustically telemetering information from the bottom of a borehole without interrupting the drilling operation. These systems utilize shear, compressional, and torsional waves along the drill string as the acoustic information carrier and all must extract an acoustic signal from acoustic noise generated by the drilling process. This noise includes: noise generated by equipment on the drilling platform and transmitted into the drill string through connections to the kelly; noise generated in the drilling mud and coupled into the drill string; noise generated by the drilling bit and transmitted into the drill string through the coupling between the drilling bit and the drill string; and noise generated by the drill string contacts with the side of the borehole. These noise sources generate a noise spectrum containing both discrete noise frequency, as that generated by the rotating drill, and random impulse noise giving rise to a continuous spectrum which may be generated by the impacting of the drill string against the side of the borehole. Most of this noise is concentrated at relatively low frequencies with a roll-off of the noise amplitude as the frequency increases. It is the intent of this invention to utilize the frequency spectrum above the concentrated noise for communications from between down-hole and the surface.